How many feet is 312 square feet?

Answer 1

None, since there can be no conversion. A foot is a measure of length in 1-dimensional space while a square foot is a measure of area in 2-dimensional space. The two measure different characteristics and, according to the most basic principles of dimensional analysis, any attempt at comparisons or conversions between the two are fundamentally flawed.

Answer 2

24 × 13 = 312 sq ft (obviously, 24 x 13 is only one possibility).